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Subject:  Re: Open question: What to put into a new house? Date:  3/9/2004  2:14 PM
Author:  MurrayS Number:  47461 of 137404

<<<Condensation and ice on the windows resulting in mold on the main level, mold on items stored in the basement.>>>

At first glance, that sounds more like a basement moisture problem than humidity from showers, etc.

Not at all. The window condensation is upstairs and the relative humidity in a basement will always be higher in the summer since it's naturally cooler without removing moisture. We've never had a drop of water in our basement.

I've not had any condensation issues at 60% humidity.

Not any issues that you can see, anyway. At 68 deg F and 60% RH, the dew point in your house is 53 deg F meaning that water will condense on surfaces below 53 degrees. That means any air that might leak into your walls from the inside and comes in contact with cold surfaces will get wet and potentially grow mold or other nasties. Obviously, you have better windows than we do or your outside temps don't dip much below freezing.

At 68 deg F and 40% RH, the dew point drops to 41 deg F. We've had ice on our windows during some of the colder nights, so obviously, the surface temperature is well below 41 deg F.

Keeping the humidity toward the 60% range increases comfort and decreases heating costs in the winter

I agree that higher humidity will make you more comfortable, but you may be destroying your walls from the inside. I found this on an EPA website:

Do not humidify to indoor relative humidity levels exceeding 50 percent. Higher humidity levels may encourage the growth of biological organisms in the home.

and this:

Operate a dehumidifier in the basement if needed to keep relative humidity levels between 30 - 50 percent

You can google “recommended humidity levels” and I doubt you will find any sites recommending 60% RH.

Again, with modern tighter houses, mold is a much greater problem than it used to be. Putting in a central dehumidifier for your basement is cheap insurance against tearing out your walls and carpeting.


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